Assessment of the Pharmacopeial Analytical Methodologies in the Dissolution Test of Enteric-Coated Lansoprazole Preparations

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1 dx.doi.org/ /dt230216p22 Assessment of the Phrmcopeil Anlyticl Methodologies in the Dissolution Test of Enteric-Coted Lnsoprzole Preprtions Al M. Abu Hmmd, Imd I. Hmdn*, nd Din El-Sbwi Fculty of Phrmcy, The University of Jordn, Ammn 11942, Jordn e-mil: ABSTRACT The performnce of the nlyticl methodologies recommended by the United Sttes Phrmcopoei (USP) monogrph (1) for dissolution testing of lnsoprzole (LPZ) enteric-coted solid dosge forms (cpsules/tblets) ws criticlly evluted. While USP dopts n essentilly nonselective UV method, the British Phrmcopoei (2) recommends highperformnce liquid chromtogrphy (HPLC) method cpble of seprting the drug from its cid degrdtion products. For n cid-lbile drug such s LPZ, one might think tht the nonselective UV method might over- or underestimte the percentge relesed becuse the degrdtion product might hve UV bsorptivity different from tht of the prent drug. We subjected six commercil products in ddition to the reference product (G) to nlysis ccording to the USP ssy nd dissolution recommendtions. Products were lso subjected to dissolution tests whereby selective HPLC method ws employed for quntifying the percentge relese. All products pssed USP ssy tests. For dissolution, the UV method dopted by USP ws more relible becuse it indicted the ctul percentge relesed compred with the selective HPLC method, which reflected only the percentge of relesed LPZ tht remined intct (undegrded). Only one product (E) filed to stisfy the USP requirements for dissolution. KEYWORDS: Lnsoprzole; dissolution; cid lbile; phrmcopei; qulity. INTRODUCTION L nsoprzole (LPZ, shown in Figure 1) is proton-pump inhibitor tht cn be given orlly nd is indicted for the tretment nd control of cid-relted diseses such s gstro-duodenl ulcers nd reflux esophgitis (3). LPZ is known for its chemicl instbility in cidic medi nd is, therefore, usully mnufctured in the form of enteric-coted tblets or pellets in cpsules (4). According to the dt presented by Gupt et l. (4), drmtic increse in the degrdtion rte of LPZ ws observed s the ph dropped only one ph unit from 6 to 5. LPZ hs been quntittively determined in formultions using different Figure 1. Chemicl structure of lnsoprzole (LPZ). nlyticl methods including spectrophotometry, highperformnce liquid chromtogrphy (HPLC), nd thinlyer chromtogrphy (5 14). LPZ is n officil drug in both the USP (1) nd the British Phrmcopoei (2) where monogrphs re vilble for ech of the rw mteril nd delyed-relese cpsules. Both the USP nd BP dopt chromtogrphic HPLC methods tht shre some prmeters (e.g., mobile phse composition employed for ssy of cpsules), but they differ in others (e.g., the sttionry phse chemistry nd the use of internl versus externl stndrds). Both the USP nd BP require the performnce of dissolution testing for the finished products over two stges (cidic nd nerly neutrl). Dissolution tests commonly employ UV spectroscopic method becuse of simplicity of the method nd bsence of usul interferences from the formultion components. However, in some cses where the drug is cid lbile, the degrdtion might be fst enough so tht the resultnt degrdtion products interfere with the simple nonselective UV procedure (15). Such potentilly serious effect on the overll dissolution results hs been demonstrted for moxicillin cpsules (16). Concerning dissolution testing of LPZ; the *Corresponding uthor. 22 MAY 2016

2 USP (1) dopts UV spectroscopic method while the BP (2) dopts more selective HPLC method. Becuse LPZ rpidly degrdes in cidic medium, the use of nonselective UV method could be potentilly risky nd my led to inccurte conclusions bout the percentge of drug tht is ctully relesed. This study ims to criticlly ssess the nonselective nlyticl method recommended by the USP (UV spectroscopy) for dissolution testing of LPZ entericcoted solid preprtions in comprison to selective HPLC method such s tht recommended by the BP. EXPERIMENTAL Mterils nd Equipment Working stndrds of LPZ were obtined from the Jordnin Phrmceuticl Mnufcturing Compny (JPM) with potency of 99.8%. HPLC grde cetonitrile, trimethylmine, nd methnol were obtined from TEDIA (USA). The internl stndrd (4-ethoxycetophenone) nd other regents were obtined from Sigm Aldrich (Germny). All solid dosge forms of LPZ commercilly vilble in the Jordnin mrket were purchsed from locl phrmcies (Tble 1). Tble 1. Detils of the Tested Preprtions of Lnsoprzole Commercil lnsoprzole preprtion code Dosge Form Btch Number Production-Expiry Dtes A tblet / /2015 B cpsule / /2016 C cpsule / /2014 D cpsule / /2015 E cpsule / /2014 F cpsule / /2016 G cpsule 2D07C 05/ /2014 All contined 30 mg/unit A Merck Hitchi HPLC system (model L-7400, Tokyo, Jpn) consisting of UV detector nd n isocrtic pump ws used. Chromtogrms were monitored nd integrted using Clrity Light softwre. A typicl C18 column (5 μm, mm, Thermo Scientific, USA) s recommended by the USP ws employed. All spectroscopic mesurements were mde using 1-cm qurtz cells on Spectroscn 80D, UV vis spectrophotometer (Biotech Engineering Mngement Co. Ltd, UK). Anlyticl Procedures USP Assy Procedure The commercil preprtions were subjected to the officil USP ssy test to verify their content before performing dissolution tests. The USP procedure ws strictly followed, nd highlight of the mjor points is described below. The wvelength of detection ws 285 nm, nd the mobile phse consisted of 1:40:60 triethylmine/cetonitrile/ph 10.5 orthophosphoric cid in wter djusted to ph 7 nd pumped t rte of 1 ml/ min. Test solutions (known s ssy preprtions) were prepred three times for ech commercil product nd injected five times onto the HPLC. Stndrd preprtions were mde by mixing 25 ml of stndrd LPZ solution (3 mg/ml in 0.1 M NOH/cetonitrile in rtio of 3:2) with 5 ml of internl stndrd solution (7.5 mg/ml), diluting to volume of 50 ml, nd further diluting 3 ml of the mixture to 50 ml. Thus, the finl stndrd preprtion mixture contined 90 nd 45 μg/ml of LPZ nd internl stndrd, respectively, which re the sme concentrtions expected for the ssy preprtions. Detils of Dissolution Tests Dissolution tests were performed per the USP monogrph using Apprtus 2 with pddle rottion speed set t 75 rpm. Six units from ech product were subjected to the dissolution test. Dissolution ws performed t two stges for ll products, the cid stge followed by the buffer stge. The first cid stge medium consisted of 500 ml of 0.1 M hydrochloric cid (HCl). Smpling t this stge ws mde t 60 min by withdrwing 25-mL liquot then proceeding directly to the second buffer stge by dding 425 ml of buffer concentrte to the remining 475 ml cid stge medium so tht the totl buffer stge volume would be 900 ml. The buffer concentrte ws prepred by trnsferring 65.4 g of monobsic sodium phosphte, 28.2 g of sodium hydroxide, nd 12 g of sodium dodecyl sulfte to suitble continer nd dding enough wter to dissolve, then diluting with wter to 4 L. While the USP monogrph requires one smple to be tken from the buffer stge t 60 min, in this study smples were obtined t 30, 60, nd 90 min. The mount of LPZ dissolved in ll tests smples ws determined by employing the USP-recommended UV spectroscopic method s follows. For the cid stge smple, bsorption t the wvelength of mximum bsorbnce (306 nm) ws mesured using the cid-stge medium s blnk nd compred with stndrd of LPZ solution (5 μg/ ml) in 0.1 M HCl. For the buffer stge, the bsorbnce of smples ws determined using the difference between bsorbnces t the wvelengths of 286 nd 650 nm using MAY

3 blnk solution composed of cid stge medium nd buffer concentrte djusted to ph 6.8 (volume rtio 19:17) nd compred with stndrd solution of LPZ (23.3 μg/ ml). Five clibrtion solutions were prepred to contin μg/ml of LPZ in 0.1 M HCl for the cid stge nd 6 30 μg/ml for the buffer stge to ensure linerity of the response in ech cse. In ddition to the bove-detiled UV method, the concentrtions of LPZ in dissolution smples (cid or buffer stges) were lso determined using n HPLC method. The chromtogrphic method employed ws essentilly tht recommended by the USP for the ssy procedure fter being dpted for the dissolution smples s follows. Ech 2-mL dissolution smple ws mixed with 2 ml of internl stndrd solution (30 μg/ ml of 4-ethoxycetophenone) nd diluted to volume of 10 ml using USP diluents before it ws injected onto the HPLC. Clcultion of the dissolved concentrtion of LPZ ws chieved by compring the pek re rtio of LPZ to the internl stndrd in the smple nd similrly prepred stndrd solution. RESULTS AND DISCUSSION Assy Vlues To properly evlute the chrcteristic relese performnce of the different products, the content of LPZ ws determined ccording to the proper ssy procedure recommended by the USP. As prt of system suitbility test, the USP requires tht the resolution between LPZ nd internl stndrd must be greter thn 5 nd the reltive stndrd devition (RSD) of multiple injections less thn 2%. Therefore, before ny nlysis nd dt collection, we ensured tht this essentil requirement ws chieved nd mintined over the period of nlysis. A smple chromtogrm for the system suitbility test resolution solution is shown in Figure 2. The obtined verge percentge per lbel nd corresponding RSD vlues for ll tested products re listed in Tble 2. Generlly, the Figure 2. Smple chromtogrm for the stndrd preprtion solution contining LPZ (t 7.7 min) nd the internl stndrd (t 12.1 min) ccording to the USP method. obtined RSD vlues were resonbly low, nd thus reproducibility could be judged s stisfctory. However, the RSD vlue for the product (A) ws notbly higher (3.8) thn the rest of the preprtions, which might reflect some vrition within the product. Nevertheless, ll products pssed the USP ssy test becuse the mount of LPZ per lbel ws lwys within the rnge stted by the monogrph (i.e., % of lbel clim). Tble 2. Averge USP Assy Results for Commercil LPZ Products (n = 6) LPZ Cpsules/Tblets Lbel (%) USP Assy Test Results RSD A B C D E F G Dissolution The USP doption of the rther nonselective UV method for the determintion of the cid-lbile drug LPZ in dissolution medium ws mjor motivtion for this work. Tht is becuse the test result might be seriously ffected by the rpid degrdtion of the relesed LPZ in the strong cidic medium. In the test, the cpsule/tblet is plced in two successive medi, the cid stge nd the buffer stge, which re 0.1 M HCl solution nd phosphte buffer (finl ph of 6.8), respectively. Only one smple is withdrwn t the end of the cid stge (60 min), nd the concentrtion of LPZ is determined by direct mesurement of bsorbnce t 306 nm nd comprison with similrly prepred stndrd solution, where no more thn 10% of LPZ should hve been relesed. The mount of LPZ relesed in the buffer stge ws determined in the sme wy s the cid stge using the proper blnk solution nd tking the difference in bsorbnce between 286 nd 650 nm insted of single bsorbnce vlue t 306 nm. The mount of LPZ relesed should not be less thn 80% in the buffer stge t 60 min. To ensure tht ll obtined bsorbnce vlues from the dissolution test were in the liner response rnge, two clibrtion curves were constructed for the cidic nd buffer stges covering the concentrtion rnges of μg/ml nd 6 30 μg/ml, which represent relese percentges of % nd %, respectively. Typicl linerity equtions of y = 0.017x nd y 24 MAY 2016

4 = 0.029x were obtined for the cid nd buffer stges, respectively, with correltion coefficients of in both cses. It should be noted, however, tht t the expected vlues of relese of less thn 10% in the cid stge, the nticipted bsorbnce vlues would be quite low (less thn 0.1), which, while within the liner response rnge, is susceptible to vrition (i.e., imprecision, which might explin the high stndrd devition vlues for the obtined percent relese of products in cidic medium, s discussed lter). Results for the dissolution test pplying the recommended USP UV method in cidic nd buffer stges re shown in Tble 3. With the exception of the product (E), which exhibited percentge relese of 13% in cid stge, ll other products exhibited percentge relese significntly less thn the llowed limit of 10%. Therefore, it could be concluded tht the product (E) is the only product tht might hve filed the requirements of the dissolution test. It should be noted tht RSD vlues were significntly high for the percentge relese vlues obtined in the cid stge unlike those for the buffer stge, which is most likely result of the very low concentrtions relesed nd the ssocited low vlues of bsorbnce ( ) in cidic medium. However, it is expected tht if the percentge relese for product reched the specified limit of 10%, high enough bsorbnce would be recorded nd the vrition, s given by RSD, would be minimized. Thus it might be rgued tht the high vrition observed would not ctully ffect the finl decision regrding the percentge relesed since it is most significnt t the very low percentges relesed (i.e., fr from the limit of 10%). Tble 3. Averge Percentge LPZ Relese (n = 6) Using the USP Method (UV) Product Tested Acid Stge b Averge Percentge LPZ Relesed Buffer stge 30 min 60 min 90 min A 0.58 (0.96) (10.3) (7.4) 99.3 (3.9) B 1.80 (1.33) 94 (8.8) (6.1) (2.8) C 0.95 (0.38) 98.6 (2.6) (1.5) (1.7) D 3.41 (1.49) 98.2 (9.2) 99.3 (7.4) (6.4) E 13.0 (2.5) 84.6 (6.6) 94.5 (5.7) 93.9 (5.0) F 3.74 (1.16) 90.6 (6.2) 97.9 (3.9) 93.2 (3.5) G 1.14 (1.01) 92.7 (3.2) 99.1 (4.8) (4.9) Note tht USP requires mesurement t 60 min only. b RSD or SD vlues shown in prentheses. For the buffer stge, ll products stisfied the USP requirements (i.e., relese of greter thn 80% t 60 min). Although the USP requirements do not include smpling t other thn 60 min, results in Tble 3 show the percentge relese for different products fter 30, 60, nd 90 min of dissolution. Differences in the performnce of the products could best be seen t 30 min, while t lter times (60 nd 90 min), ll products chieved mximum relese ner 100%. According to dt in Tble 3 nd t 30 min of dissolution, while one product relesed s high s 103.1%, nother showed only 84.6% relese (i.e., %). Tht rnge becme nrrower when percentge relese ws evluted t 60 min (95 105%). Thus it might be dvisble to evlute dissolution t 30 min insted of 60 min for the purpose of compring relese properties of different preprtions. Dissolution Test Applying HPLC Method Dissolution smples for ll products in the two stges were ssyed using n HPLC method in ddition to the USP-recommended UV method described erlier. The HPLC method ws bsed on tht recommended by the USP monogrph for the ssy of LPZ cpsules/tblets. Only the smple preprtion step ws modified to suit the nture of the dissolution smple in terms of the nlyte s well s the ph of the medium (cidic ph 1.2 or buffer ph 6.8). Exct detils for smple preprtion were discussed erlier. A stndrd solution ws lso prepred to contin the internl stndrd 4-ethoxycetophenone, which is the sme internl stndrd recommended by the USP procedure for the quntittive ssy test. As prt of vlidtion of the modified HPLC method, clibrtion curves were prepred for ech of the cid nd buffer stges nd linerity exmined. For the cidic stge, concentrtions in the rnge of 1 30 μg/ml were used, which correspond to % relese of the theoreticl idel content. For the buffer stge, concentrtions in the rnge of 1 30 μg/ml were used, which correspond to 3 100% relese of the theoreticl idel content. Typicl clibrtion equtions for cidic nd buffer stges were y = 0.020x (R 2 = 0.976) nd y = 0.032x (R 2 = 0.994), respectively. Other vlidtion prmeters of precision nd ccurcy t low nd high concentrtions were lso stisfctory. The obtined verge percentge relesed for ll products tested using the HPLC method (Tble 4) stisfied USP requirements for dissolution (i.e., relese of not less thn 80% in the buffer stge t 60 min nd not more thn 10% in the cid stge). However, one product (E) relesed the lowest percentge of LPZ s it relesed 75% nd 87% t 30 nd 60 min, respectively. Tht is consistent with the observtion tht product (E) ws the only one tht relesed greter thn 10% in the initil cid stge (i.e., lrger mount of the drug ws exposed for longer time to the cidic environment with the consequent MAY

5 higher percentge of degrdtion). The obtined percentge relese for the product (E) t 60 min using the HPLC method ws significntly lower (87.3%) thn tht obtined by the UV method (94.5%). The observed low percentge relesed here could not be simply ttributed to lower-thn-expected content of LPZ in the preprtion becuse it ws concluded to be stisfctory ccording to USP ssy results discussed erlier (97.84%). However, it could be explined in terms of degrdtion of the drug in the cidic medium nd the selective nture of the HPLC method, which selectively determined only LPZ, while the nonselective UV method determined both LPZ nd its potentil degrdtion product. If the bsorptivity of the degrdtion product t the mesuring wvelength ws significntly different from tht of LPZ, then serious error in the estimted percentge relese might be nticipted when employing the UV method (15). To further investigte potentil interferences with the UV method, the bsorption chrcteristics of LPZ nd its degrdtion product were investigted. A solution of LPZ ws prepred t concentrtion ner the limit of 10% relese from one cpsule in the employed cidic dissolution medium, which is 15 μg/ml in 0.1 M HCl, nd spectr recorded over time (Figure 3). Tble 4. Averge Percentge LPZ Relese (n = 6) Using HPLC Method Product Tested Acid Stge b % LPZ Relesed Buffer stge 30 min 60 min 90 min A < (10.3) (7.4) 99.3 (3.9) B < (10.3) (3.8) (2.3) C < (3.5) (3.9) 99.4 (6.7) D < (5.6) 94.5 (3.9) 90.2 (6.7) E 3.7 (0.71) b 75.4 (7.9) 87.3 (6.5) 83.4 (4.8) F < (6.2) 97.9 (3.9) 93.2 (6.5) G < (5.3) (6.7) (7.7) Note tht USP requires mesurement t 60 min only. b RSD or SD vlues shown in prentheses. The overlid UV spectr show mximum bsorption (λ mx ) t 338 nm tht progressively decresed with time while the minimum bsorption t bout 260 nm incresed, suggesting degrdtion ws tking plce. The 306 nm wvelength (which ws recommended by USP s λ mx ) ws n isobestic point (but not λ mx ) t which the bsorbnce remins lmost constnt with time, despite other cler chnges in the obtined spectr (Figure 3); this reflects the occurrence of degrdtion. Therefore, lthough degrdtion ws tking plce, the bsorbnce Scn Spectrum Curve Wvelength (nm) Figure 3. Overlid UV spectr of LPZ solution (15 μg/ml) recorded t 10-min intervls (time increses ccording to the direction of the rrow). Note the isosbestic point t 306 nm where the bsorbnce does not chnge despite degrdtion. vlue t 306 nm did not chnge, nd consequently, the clculted concentrtion of the dissolved drug would still be correct. Therefore, the USP method ppers to be more pproprite in this context thn selective HPLC method, becuse in dissolution experiments, the min concern would be the overll mount of drug dissolved regrdless of whether it remined chemiclly intct in the medium. These findings demonstrte tht borderline products such s product (E) might be inppropritely rejected using selective HPLC method like the one recommended by the BP, but ccepted using the rther nonselective UV method recommended by the USP. A T-test ws performed to check for significnt difference between the results obtined from the two methods (HPLC nd UV) t both stges (cidic, 60 min; buffer, 60 min) for ll products. Results for this test re listed in Tble 5. For the cidic stge, the two methods produced sttisticlly different results where only one out of the seven products tested showed similr results, with the vlues obtined by the HPLC method being generlly less thn those of the UV method. At lest in prt, this could be explined s result of the low precision of the UV method t very low bsorbnce vlues encountered when only low percentge of LPZ is relesed. For the buffer stge, however, where the error in the UV method ws minimized due to the relese of significnt mount of drug, the results obtined by both methods re lmost similr with the exception of one product (E), which repetedly showed significnt relese of LPZ in the cidic stge nd consequently degrded, leding to significnt differences in the results obtined by the UV nd HPLC methods. Thus, for products tht do not relese significnt percentge of the drug in the cidic stge with the consequence of no significnt degrdtion of LPZ, no significnt difference between 26 MAY 2016

6 the results of the HPLC or UV methods is expected. Nevertheless, this work demonstrtes with n ctul exmple of commercilly vilble product tht the nlyticl methodology employed might ffect the finl conclusion. A solid understnding of the principles of phrmcopeil nlyticl procedures is importnt. For exmple, n nlyst who does not understnd the role of the isosbestic point s wvelength of detection in LPZ in UV quntifiction method might not fully pprecite the dnger of chnging the wvelength of mesurement. Tble 5. T-Test Vlues nd p Vlues (in prentheses) for Compring the Two Methods (HPLC nd UV) t the Two Stges Product Clculted t p < Acidic Stge t 60 min Buffer Stge t 60 min A (0.0906) (0.2349) B (0.0079) (0.1144) C ( ) (0.5219) D (0.0015) (0.1831) E (< ) (0.0395) F (0.0003) (0.9514) G (0.0201) (0.6028) CONCLUSION All products tested stisfied the USP quntittive ssy requirement for drug content. The selective chromtogrphic USP ssy procedure ws dpted nd vlidted for the nlysis of dissolution smples of LPZ in cidic nd buffer medi. The dt obtined when pplying both the nonselective UV method recommended by the USP together with the dpted, more selective HPLC method, leds to the conclusion tht the recommended USP method (UV method) is more relible nd cn give the ctul percentge relesed, while the HPLC method reflects only the percentge of LPZ tht remins intct. Thus, the more selective HPLC method will show lower percentge relesed thn wht is ctully relesed for products tht relese significnt percentge of LPZ in the cid stge. Some of the relesed LPZ my degrde rpidly in the medium so tht the degrded portion my not be ccounted for by the HPLC method, lthough it is relly prt of the dissolved mount. Only one commercil product (E) filed to stisfy the USP requirements for dissolution. The rther preliminry dt presented should encourge further reserch to confirm our findings. Perhps it is pproprite to recommend to other regultory uthorities who still dopt selective HPLC methods for dissolution evlutions of LPZ products (e.g., the BP) to revise their monogrphs. ACKNOWLEDGMENT The uthors wish to thnk the Denship of Acdemic Reserch t The University of Jordn for finncil support. CONFLICT OF INTEREST No conflict of interest hs been declred by the uthors. REFERENCES 1. Lnsoprzole Monogrph. In The United Sttes Phrmcopei nd Ntionl Formulry USP 36 NF 31; The United Sttes Phrmcopeil Convention, Inc.: Rockville, MD, Lnsoprzole Monogrph. In British Phrmcopoei; The Sttionry Office: London, Stoh, H. Discovery nd Development of Proton Pump Inhibitors. In Proton Pump Inhibitors: A Blnced View; Chib, T., Mlfertheiner, P., Stoh, H., Eds.; Frontiers of Gstrointestinl Reserch, Vol. 32; Krger: Bsel, 2013; pp DOI: / Gupt, H. P.; Sini, K.; Dhingr, P.; Pndey, R. Study of Acid Ctlyzed Rections of Proton Pump Inhibitors t D.M.E. Port. Electrochim. Act 2008, 26 (5), DOI: /pe Whbi, A.-A. M.; Abdel-Rzk, O.; Gzy, A. A.; Mhgoub, H.; Moneeb, M. S. Spectrophotometric determintion of omeprzole, lnsoprzole nd pntoprzole in phrmceuticl formultions. J. Phrm. Biomed. Anl. 2002, 30 (4), DOI: /S (02) Bsvih, K.; Rmkrishn, V.; Anil kumr, U. R.; Somshekr, B. C. Spectrophotometric determintion of lnsoprzole in phrmceuticls using bromte bromide mixture bsed on redox nd complextion rections. Eclétic Quím. 2007, 32 (1), DOI: /S Devi, P. U.; Krishn, K. M. Visible Spectrophotometric Determintion of Lnsoprzole in Pure nd Phrmceuticl Formultions. Am. J. PhrmTech Res. 2013, 3 (2), Moustf, A. A. M. Spectrophotometric methods for the determintion of lnsoprzole nd pntoprzole sodium sesquihydrte. J. Phrm. Biomed. Anl. 2000, 22 (1), DOI: /S (99) Prsnn Kumr Reddy, B.; Rmnjney Reddy, Y.; Rmchndrn, D. Determintion of Pntoprzole Sodium nd Lnsoprzole in Individul Tblet Dosge Forms by RP HPLC using single mobile phse. E-J. Chem. 2009, 6 (2), DOI: /2009/ Luo, Y.; Xu, L.; Xu, M.; Feng, J.; Tng, X. A vlidted, specific, stbility-indicting HPLC method for MAY

7 determintion of lnsoprzole enteric cpsules nd relted impurities. Asin J. Phrm. Sci. 2012, 7 (2), Kumr, S. M.; Kumr, D. S.; Rjkumr, T.; Kumr, E. U.; Geeth, A. S.; Diwedi, D. Development nd vlidtion of RP HPLC method for the estimtion of lnsoprzole in tblet dosge form. J. Chem. Phrm. Res. 2010, 2 (6), Ptel, B.; Dedni, Z.; Dedni, R.; Rmoli, C.; Vidy Sgr, G.; Meht, R. S. Simultneous Estimtion of Lnsoprzole nd Domperidone in Combined Dosge Form by RP HPLC. Asin J. Res. Chem. 2009, 2 (2), Yeniceli, D.; Dogrukol-Ak, D.; Tuncel, M. Determintion of lnsoprzole in phrmceuticl cpsules by flow injection nlysis using UV detection. J. Phrm. Biomed. Anl. 2004, 36 (1), DOI: /j. jpb Dogrukol-Ak, D.; Tuncel, M.; Aboul-Enein, H. Y. The Determintion of Lnsoprzole in Phrmceuticl Preprtion by cpillry Electrophoresis. Chromtogrphi 2001, 54 (7 8), DOI: /BF Tokumur, T.; Mchid, Y. UV bsorption method should not be pplied for determining moxycillin in cidic dissolution test medium. Int. J. Phrm. 2001, 228 (1 2), 1 4. DOI: /S (01) Tpi-Albrrn, M.; Villfuerte-Robles, L. Assy of moxicillin sustined relese from mtrix tblets contining different proportions of Crbopol 971P NF. Int. J. Phrm. 2004, 273 (1 2), DOI: /j.ijphrm MAY 2016